Apparatus and method for interworking between MPLS network and non-MPLS network

ABSTRACT

In a device that interworks a VLAN network and an MPLS network, a VLAN ID is associated with an MPLS label. In a device that performs interworking from a VLAN network to an MPLS network, an output MPLS label is determined from a pair of a VLAN ID and the information in the layer 3 or layer 4 header of a packet. The output MPLS label is assigned an independent value for each VLAN. In a device that performs interworking from the MPLS network to another VLAN network, the input MPLS label is associated with a VLAN ID.

The present application is a continuation of application Ser. No.09/780,413, filed Feb. 12, 2001, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to packet communication devices,especially devices that interwork virtual private networks (VPNs).

On of the means of building an intranet in a company is a virtual localarea network (VLAN). The IEEE 802 committee of the United States hasstandardized the VLAN method as IEEE 802.10.

FIG. 2 shows the VLAN packet format as defined in IEEE 802.1Q. In a VLAN15 as defined by IEEE 802.1Q, an Internet Protocol (IP) packet 500 istransmitted as an Ethernet frame 510, in which tag control information514 is specified. User priority 514-1, Conical Format Indicator (CFI)514-2 and a 12-bit VLAN ID 5-14-3 is set in the tag control information514. The VLAN ID is the identifier of the group that configures theVLAN. A 3-bit user priority 514-1 indicates the packet priority. The IPpacket 500 also includes destination MAC address 511, source MAC address512, Tag Protocol Identifier (TPID) 513, Internet Protocol (IP) header501, IP Payload 502 and Frame Check Sequence (FCS) 515.

FIG. 3 shows a configuration example of a VLAN network. In FIG. 3, thenetwork physically extends across two locations 6-1 and 3-2, like thefirst floor and second floor of a building. Location 6-1 contains twonetworks, VLAN #A (7-1-1) and VLAN #8 (7-2-1). Location 6-2 alsocontains two networks, VLAN #A (7-1-2) and VLAN #8 (7-2-2). VLAN #A(7-1-1) and VLAN #B (7-2-1) are multiplexed by a switching hub 2-1.Similarly, VLAN #A (7-1-2) and VLAN #B (7-2-2) are multiplexed by aswitching hub 2-2. VLAN #A and VLAN #B are each assigned a unique VLANID. The switching hubs 2-1 and 2-2 identify the VLAN to which a packetbelongs, by looking at the VLAN ID. For example, packets that VLAN#A7-1-1 transmits to location 6-2 are transferred only to VLAN #A7-1-2by the switching hub 2-2.

On the other hand, one of the packet transfer technologies used in theInternet is multiprotocol label switching (MPLS). With MPLS, the packettransfer devices in a network perform packet transfer processing byusing fixed-length connection identifiers ca led labels.

FIG. 7 shows a configuration example of an MPLS network. The transfer ofa packet from terminal 4-A to terminal 4-C is explained Terminals 4-8and 4-D are also shown as being part of the network, however notransfers to them are shown. From the destination IP address that is setin the packet, device 3-1, which is the ingress node of the MPLSnetwork, determines the output destination of the packet and the labelvalue to be specified in the packet. Device 3-2, which relays thepacket, determines the output destination of the packet and the labelvalue to be specified in the output packet, by using the label that wasspecified in the input packet. Device 3-3, which is the egress node ofthe MPLS network, removes the label from the packet, looks at the IPheader that was set in the packet, and determines the next hop of thepacket. Regarding the MPLS protocol, the Internet Engineering Task Force(IETF) is working on its standardization.

FIG. 4 shows the MPLS packet format when the Point-to-Point Protocol(PPP) 20 is used as the lower layer. In PPP-based MPLS, a four-byte shimheader 522 is inserted between the PPP header 521 and the IP header 601.The shim header has a 20-bit label 521-1, a 3-bit Exp (Experimental)field 521-2, a 1-bit S bit 521-3, and an 8-bit Time to Live (TTL) field521-4. The IETF is studying whether the Exp field 521-2 should be usedas a Quality of Service (QoS) class. The MPLS packet format alsoincludes an IF Payload 602 and a FCS 523.

FIG. 5 shows the MPLS packet format when the Asynchronous Transfer Mode(ATM) is used as the lower layer. A padding 535-1 and a trailer 535-2are added to the IP packet 600 to form the AAL5 frame 535 (nullencapsulation defined according to RFC2684 of IETF). The AAL5 frame 535is divided into 48-byte sections, and the individual sections are eachgiven a cell header 531 and payload 532 and become ATM cells 530-1 to630-n.

FIG. 6 shows the ATM cell format. In ATM-based MPLS, the set values forthe virtual path identifier (VPI) 531-2 and virtual channel identifier(VCI) 531-3 in the cell header 531 are used as the label. Also, theone-bit cell loss priority (CLP) bit 531-5 10 indicates the cell discardpriority. The ATM cell format also includes a Generic Flow Control (GFC)531-1, Payload Time Identifier (PTI) 631-4 and Header Error Code (HEC)531-6.

Hereinafter, either the shim header or the ATM cell header in which thelabel value is set is called the MPLS header.

In the past, communication between physically separated offices in thesame company was generally carried out through leased lines. In recentyears, however, the number of users who connect offices by buildingvirtual private networks (VPNs) that use the Internet is increasing.

When VLANs located in physically separated places are connected throughan MPLS network, the device positioned at the ingress rode of the MPLSnetwork deletes the tag control information. Consequently, theinformation (VLAN ID) that indicates the VLAN to which the packetbelongs is lost from the packet to be transferred.

Accordingly, there is a problem in which the device positioned at the ofthe MPLS network cannot set a VLAN ID for the packet to be output.

Furthermore, because the tag control information is deleted from thepacket, the priority information (user priority) of the packet is lost.Consequently, there is a problem in which the VLAN on the side thatreceives the packet cannot perform the same QoS control as the VLAN onthe side that sends the packet.

SUMMARY OF THE INVENTION

In short, in the past, mapping the information written in the header ofthe layer corresponding to layer 2 of the OSI model to the MPLS headerhad not been studied.

Accordingly, the object of the present invention is to allow mapping ofinformation written in the header of the layer corresponding to layer 2of the OSI model to the MPLS header.

The object of the present invention is to connect VLANs located atphysically separated places and belong to the same group by using anMPLS network, while maintaining the isolation of each VLAN.

Also, another object of the present invention is to carry out consistentQoS control at each end, even when VLAN networks are interworked by anMFLS network.

In the present invention, the header transformation information thatshows the correspondence between a pair of the information in theheader, which is different from the MPLS header and is added before theheader, which is the packet header used in networks in which the MPLSprotocol is not used, of the layer that corresponds to layer 3 of theOSI model (hereinafter referred to as “layer 3 header”), of the layerthat corresponds to layer 2 of the 081 model (hereinafter referred to as“layer 2 header”), and the information in said layer 3 header; and theinformation in said MPLS header, is set in packet transfer devices thatinterwork an MPLS network and networks that do not use the MPLSprotocol. The packet transfer devices transform said layer 2 header tothe MPLS header by using this information.

Also, the header transformation information that indicates thecorrespondence between a pair of said MPLS header information and saidlayer 3 header information, and said layer 2 header information is setin the packet transfer devices.

The packet transfer devices transform the MPLS header to said layer 2header by using this information.

In a preferred embodiment of the present invention, a VLAN ID and anMPLS label are associated in the devices that interwork VLAN and MPLS.The devices that perform interworking from the VLAN networks to the MPLSnetwork determine an output MPLS label from a pair of a VLAN ID andpacket header information. The output MPLS label is assigned anindependent value for each VLAN. The devices that perform interworkingfrom the MPLS network to the VLAN networks associate an input MPLS labelto a VLAN ID.

In another preferred embodiment of the present invention, the devicesthat interwork VLAN and MPLS associate the 3-bit user priority in thetag control information to the field that sets a QoS value of the MPLSheader. For PPP-based MPLS, the 3-bit user priority is mapped to the1-bit Exp field in the shim header. For ATM-based MPLS, the: 3-bit userpriority is transformed to a 1-bit CLP bit in the cell header.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that shows a configuration example of a network thatis configured using network interworking devices of the presentinvention.

FIG. 2 is a diagram that shows the VLAN packet format specified by IEEE802.1 Q.

FIG. 3 is a diagram that shows a configuration example of a VLANnetwork.

FIG. 4 is a diagram that shows the frame format of PPP-based MPLS.

FIG. 5 is a diagram that shows the frame format of ATM-based MPLS.

FIG. 6 is a diagram that shows the cell format of ATM.

FIG. 7 is a diagram that shows a configuration example of an MPLSnetwork.

FIG. 8 is a diagram that shows a configuration example of networkinterworking devices of the present invention.

FIG. 9 is a diagram that shows a configuration example of the lowerlayer processor in network interworking devices of the presentinvention.

FIG. 10 is a diagram that shows a configuration example of the processorin network interworking devices of the present invention.

FIG. 11 is a diagram that shows a configuration example of the processorin network interworking devices of the present invention.

FIG. 12 is a diagram that shows a configuration example of the searchtable that is provided in network interworking devices of the presentinvention.

FIG. 13 is a diagram that shows a configuration example of the VLAN IDsearch table that is provided in network interworking devices of thepresent invention.

FIG. 14 is a diagram that shows a configuration example of the routesearch table for an MPLS output that is provided in network interworkingdevices of the present invention.

FIG. 16 is a diagram that shows a configuration example of the MPLSlabel search table that is provided in network interworking devices ofthe present invention.

FIG. 16 is a diagram that shows a configuration example of the routesearch table for a VLAN output that is provided in network interworkingdevices of the present invention.

FIG. 17 is a diagram that shows a configuration example of the QoStransformation table for an MPLS output that is provided in networkinterworking devices of the present invention.

FIG. 18 a diagram that shows a configuration example of the QoStransformation table for a VLAN output that is provided in networkinterworking devices of the present invention.

FIG. 19 is a diagram that shows the concept of the search procedure ofthe table search engine that is provided in network interworking devicesof the present invention.

FIG. 20 is a diagram that shows the concept of the search procedure ofthe table search engine that is provided in network interworking devicesof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the preferred embodiments of the present invention will bedescribed by using drawings.

FIG. 1 shows a configuration example of a network to which the presentinvention is applied. VLAN #A comprises networks 7-1-1, 7-1-2, 7-1-3,7-1-4 and 7-1-5.

VLAN #B comprises networks 7-2-1, 7-2-2. 7-2-3, 1-2-4 and 7-2-5.Locations 6-1, 6-2, 6-3, 6-4 and 6-6 are mutually connected by art MPLSnetwork 5. The MPLS network 5 comprises network interworking devices1-1, 1-2 and 1-3, and packet relay device 3.

Below, an example of packet transfer from VLAN #A 7-1-1 to VLAN #A7-1-4, via network interworking devices 1-1 and 1-2 is described.

FIG. 8 shows a configuration example of network interworking devices1-1, 1-2 and 1-3 of the present invention. The network interworkingdevices have a lower layer processor for Ethernet 11, a packet layerprocessor 12, an lower layer processor for MPLS 13, a switch 14 and acontrol processor 15.

When the lower layer processor for Ethernet 11 receives an Ethernetframe, it performs termination processing of the physical and data linklayers of that frame and passes the IP packet and tag controlinformation to the packet layer processor 12. The lower layer processorfor Ethernet 11 also adds the destination MAC address and tag controlinformation that were determined by the packet layer processor 12 to theIP packet, changes the IP packet to an Ethernet frame, and sends it tothe VLAN network.

When the lower layer processor for MPLS 13 receives an MPLS packet, itperforms termination processing of the physical layer and MPLS header ofthat packet and passes the IP packet and MFLS header information to thepacket layer processor 12 Also, the MPLS header information that wasdetermined by the packet layer processor 12 is added to the IP packet,and the IP packet is changed to an MPLS packet and sent to the MPLSnetwork.

The packet layer processor 12 determines the next hop of the packetbased on the IP header information and tag control information of theinput packet, or the MPLS header information.

The switch 14 transmits the packet that was output from a packet layerprocessor 12 to the other packet layer processor 12 that corresponds tothe next hop of the packet specified by the first packet layer processor12.

The control processor 15 is connected with the management system andcontrols all the processors in network interworking device 1.

FIG. 9 shows the configuration of the lower layer processor for Ethernet11 that is located in the circuit on the VLAN side.

The physical layer receiver 111 performs physical layer processing of areceived Ethernet frame. The Ethernet receiver 112 performs terminationprocessing of a received Ethernet frame. Namely, based on thedestination MAC address of a received frame, all the frames addressed tolocations other than itself are discarded and also processing ofextracting the tag control information o a received frame addressed toitself is performed. The packet layer processor interfaces 113 and 114are the interfaces with the packet layer processor 12. The Ethernettransmitter 115 performs processing such as adding MAC addresses and tagcontrol information to transform an IP packet to an Ethernet frame. Thephysical layer transmitter 116 performs processing of transmitting anEthernet frame through the physical circuit. The control processorinterface 117 is the interface with the control processor 15 andconnects with all the configuration elements of the lower layerprocessor 11.

FIG. 10 shows the configuration of the packet layer processor 12. Thelower layer processor interfaces 121 and 126 are the interfaces with thelower layer processor for Ethernet 11 and the lower layer processor forMPLS, respectively. The table search engine 122 searches the tables 123and performs processing of obtaining an output physical port and VLANID, or an MPLS label to be added to an output packet. The switchinterfaces 124 and 126 are the interfaces with the switch 14. Thecontrol processor interface 127 is the interface with the controlprocessor 15 and connects with all the configuration elements of thepacket processor 12.

FIG. 12 shows a configuration example of the search table 123. Thesearch table 123 consists of a VLAN ID search table 123-1, a routesearch table 123-2 for an MPLS output, an MPLS label search table 123-3,a route search table 123-4 for a VLAN output, a QoS transformation table123-5 for an MPLS output and a QoS transformation 20 table 123-6 for aVLAN output. These search tables are constructed in memory. It is no:necessary that all the search tables are constructed in the same memory.

The VLAN ID search table 123-1 uses a VLAN ID as a search key and is thetable for determining which VLAN it belongs to by searching it. Theroute search table 123-2 for an MPLS output is the table for determiningan output label at the ingress not from the VLAN network to the MPLSnetwork. The MPLS label search table 123-3 uses an MPLS label as asearch key and is the table for determining which VLAN it belongs to.The route search table 123-4 for a WAN output is the table fordetermining an output VLAN ID at the egress node from the MPLS networkto the VLAN network. The QoS transformation table 123-5 for an MPLSoutput is the table for transforming a QoS value (user priority) of theVLAN network to a QoS value of the MPLS network. The QoS transformationtable 123-6 for a VLAN output is the table for transforming a QoS valueof the MPLS network to a QoS value (user priority) of the VLAN network.

FIG. 11 shows the configuration of the lower layer processor for MPLS13. The physical layer receiver 131 performs physical layer processingof a received packet. The MPLS receiver 132 performs terminationprocessing of the data link layer and processing of extracting the MPLSheader. The packet layer processor interfaces 133 and 134 are theinterfaces with the packet layer processor 12. The MPLS transmitter 133performs termination processing of the data link layer and processing ofadding the MPLS header to the IP packet. The physical layer transmitter136 transmits the packet to which the MPLS label has been added, throughthe physical circuit. The control processor interface 137 is theinterface with the control processor 15 and connects with all theconfiguration elements of the lower layer processor 13.

The processing procedure by which network interworking device 1associates a VLAN ID and an MPLS label is described.

The processing procedure by which network interworking device 1-1 inFIG. 1 obtains an output label from an input VLAN ID is described.

In network interworking device 1-1, the table search engine 122 searchesthe search table 123.

FIG. 19 shows the concept of the search procedure performed by the tablesearch engine 122 in network inter-working device 1-1. The table searchengine 122 first searches the VLAN ID search table 123-1 and thensearches the route search table 12:3-2 for an MPLS output.

FIG. 13 shows a configuration example of the VLAN ID search table. Inthe VL4N ID search table 123-1, the input VLAN ID 123-1-1 is set as thesearch key, and the VLAN name 123-1-2 that corresponds to the VLAN ID isset as the search result. In the example shown in FIG. 13, when the VLANID search table 123-1 is searched with a value 10 as the input VLAN ID,the result is VLAN #A. A combination of the input VLAN ID and the inputphysical port of the packet can also be used as the search key. If acombination of the input VLAN ID and the input physical port of thepacket is used as the search key, the same VLAN ID value can be used bydifferent input physical ports in a configuration that contains multiplephysical ports in the lower layer processor 11 shown in FIG. 8.

FIG. 14 shows a configuration example of the route search table for anMPLS output. In the route search table 123-2 for an MPLS output, thedestination IP address 123-2-1 is set as the search key, and the outputlabel 123-2-2 and the output physical port 123-2-3 are set as the searchresults. The entry of the route search table 123-2 for an MPLS output isdivided for each VLAN. With the example shown in FIG. 14, the routesearch table 123-2 for an MPLS output is divided into the entry 123-2-afor VLAN #A and the entry 123-2-b for VLAN #8.

If the search result for the VLAN ID search table 123-1 is VLAN #A, theentry 123-2-a of the route search table 123-2 for an MPLS output issearched. For the example shown in FIG. 14, if the entry 123-2-a issearched with the destination IP address 192.168.10.0, the resultbecomes a value 100 for the output label and output physical port 3.

Next, the processing procedure in which network interworking device 1-2in FIG. 1 obtains the output VLAN ID from the input label is described.

In network interworking device 1-2, the table search engine 122 searchesthe search table 123.

FIG. 20 shows the concept of the search procedure of the table searchengine 122 in network interworking device 1-2. The table search engine122 first searches the MPLS label search table 123-3 and then searchesthe route search table 123-4 for a VLAN output.

FIG. 15 shows a configuration example of the MPLS label search table123-3. In the MPLS label search table 123-3, the input label 123-3-1 isset as the search key, and a VLAN name that corresponds to an inputlabel is set as the search result. In the example shown in FIG. 15, whenthe MPLS label search table 123-1 is searched with an input label value101, the result is VLAN #A. A combination of an input label and an inputphysical port can also be used as the search key. If a combination of aninput label and the input physical port of a packet is used as thesearch key, the same label value can be used by different input physicalports in a configuration that contains multiple physical ports in thelower layer processor 13 shown in FIG. 8.

FIG. 16 shows a configuration example of the route search table 1234 fora VLAN output.

In the route search table 123-4 for a VLAN output, the destination IPaddress 123-4-1 is set as the search key, and the destination MACaddress 123-4-2, the output VLAN ID 123-4-3 and the output physical port123-4-4 are set as the search results. The entry of the search table123-4 is divided for each VLAN. In FIG. 16, the route search table 123-4for a VLAN output is divided into the entry 123-4-a for VLAN #A 25 andthe entry 123-4-b for VLAN #B.

If the search result for the MPLS label search table 123-3 is VLAN #A,the table search engine searches the entry 1234-a. If the entry 123-4-ais searched when the destination IP address is 192.168.10.0, the resultsbecome a value aa.bb.cc.dd.ee.ff for the output MAC address, a value 10for the output VLAN ID, and, output physical ports.

Next, the processing procedure for realizing the end-to-end QoS controlis described.

FIG. 17 shows a configuration example of the QoS transformation table123-10 for an MPLS output for mapping the user priority stipulated byVLAN to the QoS information of the MPLS header in network interworkingdevice 1-1.

In the QoS transformation table 123-10 for an MPLS output, the TCP/IPheader information 123-10-1 and the user priority 123-10-2 are set asthe search keys, and the QoS value 123-10-3 of the output MPLS header isset as the search result.

The table search engine 122 searches the QoS transformation table 123-10for an MPLS output by using the TCP/IP header information and userpriority added to the input packet as the search keys and obtains a QoSvalue to be set in the output MPLS header as the result. A destinationIP address, type of service (TOS) value of the IP header and destinationport number of the TCP header can be used as the TCP/IP headerinformation 123-10-1. In the example shown in FIG. 17, the destinationIP address is used as the TCP/IP header information 123-10-1. InPPP-based MPLS, the QoS information in the MPLS header can be associatedwith the Exp field, while in ATM-based MPLS, the QoS information can beassociated with the CLP bit in the cell header.

FIG. 18 shows a configuration example of the QoS transformation table123-11 for a VLAN output for mapping the QoS information in the MPLSheader to the user priority in network interworking device 1-2.

In the table 123-11 for a VLAN output, the TCP/IP header information123-11-1 and the input MPLS QoS value 123-11-2 are set as the searchkeys, and the user priority 123-11-3 is set as the search result.

The table search engine 122 searches the QoS transformation table 123-11for a VLAN output by using the TCP/IP header information and output MPLSQoS value added to the input packet as the search keys and obtains anoutput user priority value as the result. A destination IP address and aTOS value in the IP header can be used as the TCP/IP header information123-11-1. In the example shown in FIG. 18, the destination IP address isused as the TCP/IP header information 123-11-1. In PPP-based MPLS, theQoS information in the MPLS header can be associated with the Exp field,while in ATM-based MPLS, the QoS information can be associated with theCLP field in the cell header.

When the search of the QoS transformation table 123-10 for an MPLSoutput in network interworking device 1-1 is combined with the search ofthe QoS transformation table 123-11 for a VLAN output in networkinterworking device 1-2, a VLAN QoS value can be kept even in a networkthat uses an MPLS network to interwork VLAN networks that belong to thesame group.

Because the user priority in the VLAN tag control information and theExp bit in the shim header are both three bits, the same QoS value canbe used in the VLAN and MPLS networks. Therefore, if the lower layer inan MPLS network is PPP, the TCP/IP header does not necessarily have tobe set as the search key.

There are two methods for setting up the search table 123. One of themis performed manually by an administrator of network interworking device1. The other is performed automatically by a device in a network whichexchanges information autonomously.

An example in which an administrator of network interworking device 1sets up the search table 123 manually is described.

When an administrator of network interworking device 1 sets up thesearch table 123 manually, the administrator determines values to be setto the search table 123 based on the operation policy of the networkafter understanding the network configuration. At this time, an operatorof the VLAN network reports information necessary for connecting theVLAN networks located at physically separated places to theadministrator of network interworking device 1. An example of thatinformation is the IP address information of the devices to beconnected. The administrator of network interworking device 1 sets upthe search tables 123 by entering commands from the management systemthat is connected to the control processor 16 of network interworkingdevice 1.

An example of automatic setup of the route search table 123-2 for anMPLS output is the method that uses a signaling protocol for labeldistribution. Label distribution protocols include the LabelDistribution Protocol (LDP), which is defined indraft-ieff-mpls-ldp-06.txt of IETF, etc. When LDP is used, labels to beused through MPLS paths are assigned autonomously to the individualdevices 1-1, 1-2 and 1-3 that configure MPLS network 5, by which thesedevices exchange messages with each other.

An example of automatic setup of the search table 123-4 for a VLANoutput is the method that uses a routing protocol. The routing protocoloperates between network interworking device 1-2 and the devices thatconfigure LAN networks 7-1-3 and 7-1-4. As examples of the routingprotocol, the Open Shortest Path First (08FF), which is defined asRFC2178 of IETF, etc. are available. By using a routing protocol,network interworking device 1-2 can get the correspondence between thedestination IP address 123-4-i and the output physical port 123-4-4, andthe next hop IP address.

Furthermore, by using the Address Resolution Protocol (AEP), which isdefined by RFC82G of IETF, network interworking device 1-2 can get thecorrespondence between the next hop IP address and the MAC address123-4-2.

By the present invention, the information written in the header of thelayer corresponding to layer 2 of the OSI model can be mapped to theMPLS header.

Furthermore, by the present invention, VLAN networks located atphysically separated places can be interworked through an MPLS network,without impairing the isolation of those networks. Also the end-to-endQoS control can be performed at both ends of VLAN networks.

1. A packet transfer device that interworks a multiprotocol labelswitching (MPLS) network which uses a MPLS protocol, and a network thatdoes not use said MPLS protocol, wherein: in said MPLS network, packetswitching is performed by a MPLS header which is added before a headerof a layer corresponding to layer 3 of the Open System Interconnection(OSI) model, and in a network which does not use said MPLS protocol,packet switching is performed by a header of the layer corresponding tolayer 2 of the OSI model, which is different from said MPLS header andis added before said layer 3 header, and wherein said packet transferdevice comprises: a first physical port which receives a packet that istransmitted from the network which does not use said MPLS protocol, asecond physical port for connecting with said MPLS network, a memorythat stores header transformation information that shows correspondencebetween a pair of information in said layer 2 header and information insaid layer 3 header in correspondence with information in said MPLSheader, and a processor that searches said header transformationinformation and transforms said layer 2 header contained in a packetreceived from said first physical port to said MPLS header correspondingto said layer 2 header.